The Labour Party is a democratic socialist party. So states Clause IV, even after Blair’s rewrite. We may debate what “socialist” should mean in 2020. But there can be no dispute about the importance of democracy.

In announcing that “supporters” could pay £3 and register to vote in Labour’s leadership elections, Harriet Harman said: “We should not be afraid of differences… And nor should we be afraid of letting the public in to see [our] arguments”. She invited people to be “brutally honest about what they think of us and what they want from us”. Interestingly, the title of the speech was "Time to let the public in".

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Opening up Labour to wider participation has proven successful: there are now at least 121,000 registered supporters who have pledged that they “support the aims and values of the Labour Party”.

Yet young voters flocking to Labour, instead of being welcomed by the party’s grandees, have been told to get heart transplants. Events overflowing with first-time voters are dismissed as “madness”. Tony Blair has just said that Labour is now "in danger more mortal today than at any point in the over 100 years of its existence". The party's elites appear to have become so hypnotised by their own dogmatic notions of “electability” that they are rejecting the most essential force to win elections: voters.

Jeremy Corbyn addresses supporters from the top of a fire engine after one of his rallies spilled into the street (Lee Thomas)

In this atmosphere, it is vital to make sure that Labour's new generation of members doesn't have its hopes crushed. Labour has a rare opportunity to ward off cynicism and foster participation. This election must therefore be fair, and seen to be fair.

“Entryism” is the newest bogey in the effort to undermine the democratic framework upon which Labour launched this contest. But as Michael Crick has shown, the threat of infiltration is exaggerated. According to Crick’s analysis, entryism does not come close to accounting for the unexpected trends in this election.

The charge of rejecting entryism has fallen disproportionately on Corbyn – even though the official campaigns of all four candidates have invited non-members to sign up as supporters, and even though Corbyn has repeatedly stated that he does not welcome those who are not serious Labour supporters.

If it wasn't Corbyn who was attracting so many new voters, there would be no fuss about entryism, which has now become, in Crick’s words, a “lame excuse for backers of other candidates to explain why their man or woman isn’t winning”.

“Entryism” is being invoked as a reason to disenfranchise voters. In addition to a handful of publicity-hungry mischief-makers on the right (such as Toby Young), a number of voters who agree with Labour’s values appear to have been denied a vote. Take The Independent's very own Mark Steel, who despite campaigning door-to-door for Labour in May, has been blocked from registering with the party. And it gets worse: Labour has also said that it may void the ballots of registered supporters even after they have been returned.

All of this harms the credibility of the election. Genuine Labour supporters who have signed up are right to question the basis on which voters’ purity is being tested. For example, why is a Welsh voter who once tweeted support for Plaid Cymru’s anti-austerity platform deemed an opponent of Labour values, while the Labour MP Simon Danczuk, who has called for a coup if Corbyn wins, is regarded as an upholder of those values?

Labour is a broad church, and trying to “weed out” supporters can only damage the appearance of a fair and democratic process. In the event of a surprise result, this will only breed the perception of a stitch-up.

Credit: Getty Images

To preserve the credibility of the election, registered supporters must not be denied the vote unless it can be proved conclusively that they don't endorse Labour's aims and values.

On top of this, voters must not be retroactively disenfranchised. Once returned, ballots must not be voided because someone in a dark room has judged that the people who cast them don't subscribe to the same definition of socialism as the Peter Mandelsons of the party. Any irregularity should be resolved before the votes are cast.

And because Labour doesn't intend to publish the breakdown of votes, there must be transparency in the counting, as well as a fast-track appeals process for any invalidated ballots.

This election has activated countless young voters for the first time. If there is even a whiff of wrongdoing, an entire generation will recoil from politics. But rather than surrender to party elites who appear to be growing ever more desperate, Labour should honour the democratic process. And if that means that the establishment's least favoured candidate wins, then so be it.